This invention relates to pigment compositions useful in preparing printing inks, paints, and colored plastics. More particularly, the invention relates to a dry predispersed coated pigment composition that is immediately suitable, after simple mixing in an ink system, without milling, to give a ready-to-use printing ink. The invention also relates to a method of preparing the composition.
Prior art pigments contain, for typical black printing inks, about 20% carbon black, plus vehicle and resin (or binder), in a wet form. Usually, such a mixture is milled, such as on a 3-roll mill, for some time to obtain a well-dispersed mixture. This expensive and time-consuming milling is a major disadvantage in the present-day ink industry. Another method, according to U.S. Pat. No. 3,712,824, involves admixing, with agitation, a water slurry of a pigment with an oil-in-water emulsion containing a varnish. The mixture of organic liquid, resin and pigment is then dried, to form a dispersible pigment.
In contrast to the disadvantages found in preparing the prior art printing ink products, the present invention provides a composition that is quickly and readily mixed with a resin, solvent or oil, to form an ink system, with simple agitation and no required milling, furnishing a finished ink that is ready to use. The invention provides a composition having a high loading (approximately 90-95%) of pigment. This loading is much higher than prior art compositions, and thus furnishes the ultimate user with an economical source of pigment. Also, the present composition has been densified sufficiently to avoid the dust frequently encountered when mixing a prior art dry pigment composition with a solvent ink system. The present invention allows a printer to maintain a reasonable inventory of various dry predispersed coated pigments, separate from the various ink systems, with the various components being easily mixed to furnish the desired printing ink, without maintaining a large, expensive, cumbersome and inefficient inventory of prepared inks. Further, the printer does not need a 3-roll mill to incorporate the dry pigment of this invention into the solvent ink system, as is common with prior art pigments.